This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-003901, filed Jan. 11, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a silver halide photographic emulsion and a silver halide photographic light-sensitive material using the same. In more detail, the present invention particularly concerns a high-speed silver halide photographic emulsion whose development proceeds fast, and to a silver halide photographic light-sensitive material using the same.
2. Description of the Related Art
It is well known that to obtain a high-speed silver halide photographic light-sensitive material, tabular silver halide grains (hereinafter referred to as xe2x80x9ctabular grainsxe2x80x9d) are used. As a method for sensitizing such tabular grains, sensitizing methods using an epitaxial junction are disclosed in Jpn. Pat. Appln. KOKAI Publication No. (hereinafter referred to as JP-A-) 58-108526 and JP-A-59-133540. Further, applications of the methods to tabular grains each having a smaller thickness or a greater equivalent-circle diameter are disclosed in JP-A""s-8-69069, 8-101472, 8-101474, 8-101475, 8-171162, 8-171163, 8-101473, 8-101476, 9-211762 and 9-211763 and U.S. Pat. Nos. 5,612,176, 5,614,359, 5,629,144, 5,631,126, 5,691,127 and 5,726,007. However, the epitaxial sensitizing method, which uses silver chloride as one of the major constituents, is basically unstable as a light-sensitive material for photography fabricated using silver iodobromide as a fundamental constituent. This is because silver chloride has a solubility product greater than those of silver bromide and silver iodide and, therefore, silver halide conversion is liable to occur. Thus, a light-sensitive material in which an epitaxial emulsion is used has a drawback in that the development speed, especially that in high density portions, is slow. For this reason, epitaxial sensitization method cannot be widely used for light-sensitive materials for general photography.
The inventors of the present invention focused their attention on the fact that in conventional epitaxial emulsions, an epitaxial junction is easily broken during ripening, and the degree thereof is influenced by the halogen composition in the epitaxial portion and/or the structure of the side surfaces of the host tabular grain that receives the epitaxial junction. In conventional epitaxial emulsions using silver chloride, the silver chloride content in epitaxial junction portions is higher than 28 mol %, as described in the above-listed patents. Formation of the side surface structure of the host tabular grains is carried out by addition of an aqueous silver salt solution and an aqueous bromide salt solution. In this process, introduction of silver iodide is conducted, as described in the above-listed patents, by simultaneous addition of a silver iodide Lippmann emulsion. However, this method does not enable free control of the side surface structure of the host grains, since the dissolving speed of silver iodide emulsion grains is limited by the large size of the trains. JP-A-2-188741 discloses a method of forming host tabular grains by adding and dissolving only a silver iodobromide fine grain emulsion prepared immediately before its addition. However, this method also does not enable free control of the side surface structure of host tabular grains, because dissolution of the silver iodobromide fine grain emulsion is extremely slowed due to the increase in the content of silver iodide.
The object of the present invention is to provide a silver halide photographic emulsion capable of satisfying simultaneously both the enhancement of sensitivity and problem of delay in the development progress, the emulsion having characteristics of low fogging, high sensitivity, rapid development progress and hard gradation, and also to provide a silver halide photographic light-sensitive material using the same.
The inventors of the present invention found that instability of epitaxial emulsions can be overcome by controlling the silver chloride content in epitaxial junction portions and that the side surface structure of tabular grains can be freely controlled by forming host tabular grains by adding a silver iodobromide fine grain emulsion prepared immediately before its addition. Further, they found that when this method is used to form epitaxial junction portions, thereby to increase the (111) ratio of the side surfaces, epitaxial junctions occurred only restrictedly in apex portions of the tabular grains, resulting in an enhancement of the development speed. The inventors have accomplished the present invention through these findings.
That is, the above objects are attained by the following means (1) to (15):
(1) A silver halide photographic emulsion comprising silver iodochlorobromide tabular grains each having (111) faces as main planes thereof, wherein 70% or more of the total projected area of all the grains contained in the emulsion is occupied by grains each meeting conditions (i) to (iv) below:
(i) a hexagonal tabular grain whose ratio of the length of an edge having the maximum length with respect to the length of an edge having the minimum length, is 2 or less,
(ii) an epitaxial junction portion having a silver chloride content of 5 mol % or more and 25 mol % or less, is provided on at least one apex portion of the hexagon,
(iii) a silver chloride content thereof is 0.5 mol % or more and 6 mol % or less, and
(iv) a silver iodide content thereof is 0.5 mol % or more and 10 mol % or less.
(2) A silver halide photographic emulsion comprising silver iodochlorobromide tabular grains each having (111) faces as main planes thereof, wherein the tabular grains each having a ratio of (111) face to the side surfaces of 75% or more, and 70% or more of the total projected area of all the grains contained in the emulsion is occupied by grains each meeting conditions (i), (iixe2x80x2), (iii) and (iv) below:
(i) a hexagonal tabular grain whose ratio of the length of an edge having the maximum length with respect to the length of an edge having the minimum length, is 2 or less,
(iixe2x80x2) an epitaxial junction portion is provided on at least one apex portion of the hexagon,
(iii) a silver chloride content thereof is 0.5 mol % or more and to 6 mol % or less
(iv) a silver iodide content thereof is 0.5 mol % or more and 10 mol % or less.
(3) The silver halide photographic emulsion according to item (2), wherein the epitaxial junction portion has a silver chloride content of 5 mol % or more and 25 mol % or less.
(4) The silver halide photographic emulsion according to item (1) or (3), wherein the silver chloride content of the epitaxial junction portion is 10 mol % or more and 20 mol % or less.
(5) The silver halide photographic emulsion according to any one of items (1), (3) and (4), wherein the silver iodide content of the epitaxial junction portion is 1 mol % or more and 10 mol % or less.
(6) The silver halide photographic emulsion according to item (2) or (3), wherein the ratio of (111) face to the side surfaces is 85% or more.
(7) The silver halide photographic emulsion according to any one of items (1) to (6), wherein each of the grains occupying 70% or more of the total projected area further meeting condition (v) below:
(v) an equivalent-circle diameter thereof is 0.3 xcexcm or more and the thickness is 0.2 xcexcm or less.
(8) The silver halide photographic emulsion according to any one of items (1) to (7), wherein the variation coefficient of equivalent-circle diameters of all the grains contained in the emulsion is 30% or less.
(9) The silver halide photographic emulsion according to any one of items (1) to (8), wherein each of the grains occupying 70% or more of the total projected area further meeting condition (vi) below in addition to the conditions (i) to (iv); (i), (iixe2x80x2), (iii) and (iv); (i) to (v); or (i), (iixe2x80x2), (iii), (iv) and (v):
(vi) an equivalent-circle diameter thereof is from 0.5 xcexcm to 1.2 xcexcm and a thickness thereof is 0.1 xcexcm or less.
(10) The silver halide photographic emulsion according to any one of items (1) to (9), wherein the grains occupying 70% or more of the total projected area further meeting condition (vii) below in addition to the conditions (i) to (iv); (i), (iixe2x80x2), (iii) and (iv); (i) to (v); (i), (iixe2x80x2), (iii), (iv) and (v); (i) to (vi); (i), (iixe2x80x2), (iii), (iv), (v) and (vi):
(vii) no dislocation lines are present anywhere other than the epitaxial junction portion.
(11) The silver halide photographic emulsion according to any one of items (1) to (10), wherein host tabular grains on which the epitaxial junction portion is deposited were formed by adding a silver iodide fine grain emulsion prepared immediately before the addition thereof.
(12) The silver halide photographic emulsion according to any one of items (5) to (11), wherein the epitaxial portion was formed by adding a silver iodide fine grain emulsion prepared immediately before the addition thereof.
(13) The silver halide photographic emulsion according to item (11) or (12), wherein the grain size of the silver iodide fine grain emulsion is 0.02 xcexcm or less.
(14) The silver halide photographic emulsion according to item (13), wherein the grain size of the silver iodide fine grain emulsion is 0.01 xcexcm or less.
(15) A silver halide photographic light-sensitive material comprising a support having thereon a silver halide light-sensitive silver halide layer containing the silver halide photographic emulsion according to any one of items (1) to (14).
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.